1. Field of the Invention
This invention relates to a seal ring in which hydraulic pressure acts upon the side surface thereof, as well as to a seal device using this seal ring.
2. Description of the Prior Art
An automatic transmission employed in automotive vehicles has a hydraulic circuit which actuates clutches and brakes. A seal ring and seal device which prevent leakage of oil supplied to the hydraulic circuit are widely used. An example of a seal device using such a seal ring is illustrated in the sectional view of FIG. 5.
As shown in FIG. 5, a seal device indicated at numeral 1 has a hydraulic passageway 3 formed in a shaft 2, a pair of ring grooves 4 provided in the outer circumferential surface of the shaft 2, and seal rings 5, which are made of synthetic resin, fitted into the ring grooves 4. The peripheral surface of each seal ring 5 is brought into sliding contact with the inner peripheral surface of a rotary housing 6 on the drive side. The hydraulic passageway 3 communicates with a working chamber 9 inside the housing 6 via a groove 7 in the outer peripheral surface of the shaft 2 and an inlet 8 provided in the housing 6. A piston 10 delimits the working chamber 9 inside the housing 6. Hydraulic pressure within the working chamber 9 slides the piston 10 to the left in FIG. 5 so as to bring clutch plates 11 on the side of housing 6 and clutch plates 13 on the side of an output shaft 12 into sliding contact, thereby transmitting the rotating motion of the housing 6 to the output shaft 12. Cutting off the supply of hydraulic pressure to the working chamber 9 frees the clutches, thereby halting the transmission of rotating motion to the output shaft 12.
The groove 7 in the outer peripheral surface of the shaft 2 communicates with each of the ring grooves 4 so that hydraulic pressure that has been introduced to the ring grooves 4 brings the seal rings 5 into pressured contact with the side surfaces of the ring grooves 4 and brings the seal rings 5 into sliding contact with the inner peripheral surface of the housing 6, thereby preventing leakage of oil. In the example of FIG. 5, the forces which act upon the side surfaces of the seal rings 5 are larger than the forces which act upon the inner peripherals of the seal rings 5. As a result, the seal rings 5 are retained on the side of the shaft 2 and the outer peripheral surfaces of the seal rings 5 are brought into sliding contact with the housing 6. In this case, however, loss torque due to this sliding contact is large. Consequently, the outer circumferential surfaces of the seal rings 5 are held against the housing 6 and the side surfaces of the rings 5 are brought into sliding contact with the side wall surfaces of the ring grooves 4. An example of this is illustrated in FIG. 6.
As shown in FIG. 6, seal rings 5' each have circumferentially extending annular grooves 14 in both side surfaces thereof, and a plurality of spaced, diametrically extending grooves 15 which open to the annular grooves 14. Hydraulic pressure is introduced into the grooves 14, 15 so that each seal ring 5' is brought into sliding contact with one side wall of the respective ring groove 4 by a force P1 acting upon the side surface of the seal ring 5' and so that each seal ring 5' is held on the side of housing 6 by a force P2 acting upon the inner circumferential surface of the seal ring 5'.
In the example of FIG. 6, a sealed surface is assured over a width l.sub.1 between the side surface of each seal ring 5' and the side wall surface of the corresponding ring groove 4. However, the width l.sub.1 is small. Consequently, if the side wall surface of the ring groove 4 has been machined to have an incline (which is caused by the groove being machined at a low precision), the side wall surface wears eccentrically, the shaft 2 comes to be set off center and the rotating housing may wobble. If this occurs, the annular grooves 14 will open to the atmosphere and oil will leak out.